Amide impregnated grinding wheels



United States Patent 3,471,277 AMIDE IMPREGNATED GRINDING WHEEL RussellA. Ackermann, IL, Cincinnati, Ohio, assignor to The Cincinnati MillingMachine C0,, Cincinnati, Ohio, a corporation of Ohio No Drawing. FiledNov. 8, 1966, Ser; No. 592,741

Int. Cl. B24d 11/00 US. Cl. 51295 Claims ABSTRACT OF THE DISCLOSURE Anovel grinding wheel has been provided which comprises of abrasivegrits, a vitrified bond holding said grits together to form the grindingwheel and having its interstitial space filled essentially with an amideof a diamine and a carboxylic acid having a melting point of at least225 F. and wherein the amine precursor is an aliphatic diamine, acycloaliphatic diamine or an aromatic diamine. An improved grindingmethod has also been disclosed.

with which other ceramic materials are admixed. In preparing grindingwheels, abrasive grains and the bonding agent are mixed, shaped, driedand finally fired in a kiln to achieve a desired bond strength in amanner well known in the art. It is equally well known that vitrifiedbonds are strong, rigid, and have various degrees of porosity ordenseness.

It has been found by experience that metal chips as well as the abrasivegrains are not as readily carried away from the work piece as isdesired. Through a combination of factors, metal chips and fracturedgrains as well as other materials cause such phenomena as loading,chatter, dullness and overheating resulting in poorly finished workpiece and intolerable power consumption. These phenomena in turn requirerepeated and severe wheel dress.

Numerous attempts have been made to minimize or eliminate the problemsoccasioned by the above phenomena, and equally numerous solutions havebeen proposed for solving the above problems.

. A partial, though still unsatisfactory, solution to these problems hasbeen the introducing of various agents such as a beeswax and paraffinmixture as impregnants into the pores or interstices of grinding wheels.However, these impregnants have the tendency during the work cycle tomelt and then migrate from the wheel. Another partially satisfactorysolution has been to use the above components individually or jointly inadmixture with various sulphurized fats. Still another partiallysatisfactory solution has been the use of sulphur as a grinding wheelimpregnant.

While several possible mechanisms have been suggested to account for theimproved performance obtained using the last mentioned sulphurimpregnant, it is not possible to demonstrate or predict conclusivelywhich, if any, of the mechanisms is in fact responsible for the results.Thus, it has been suggested that chemical action takes .place betweenthe metal in the work piece and the sulphur preventing the welding ofthe metal to the wheel constituents. Another suggestion is that the hotmetal chip removed from the work piece contacts the sulphur, melts it,and then the sulphur releases the chip and allows it to be carried awayfrom the work piece. These phenomena, supposedly, prevent the loading ofthe wheel and uneven wear. However, 1t has been found that despite allattempts to introduce thoroughly and uniformly sulphur into a wheel,invariably some spaces of the wheel are not impregnated. Although thesespaces may be very small, these often cause excessive loading of thewheel with the consequent buildup of metal and thus the scoring of thework piece and failure to maintain specified tolerances. Moreover,sulphur often causes severe straining of work pieces.

'Because of the lack of understanding associated with wheel loading andwear, the utility of a particular compound suitable for filling thepores in a grinding Wheel,

in general, has to be established by experiment, Accordingly,comparative experiments have been necessary to establish the superiorityof one impregnant over another. Generally, a standard has been a sulphurimpregnated wheel compared to a wheel having an equivalent wheelstructure which wheels are used under identical or standardizedconditions.

In the present specification, the following empirical criteria will beused. As one criterion 2 work-cycle or work-piece output per dress cycleis used when using identical grit wheels. This criterion is defined asthe number of work pieces produced having satisfactory dimensions andproperties per equivalent dress. The identical operating conditions onthe identical material are observed throughout the cycle. Conversely,for the same work-piece cycle, the duration and extent of wheel dressmay be measured. Another criterion is the ability to maintain specifiedtolerances, such as surface finish and part geometry for the work piecesto be ground throughout the work cycle; e.g., under conditions usingconstant force during grinding. Still another criterion is the improvedsurface finish and absence of metallurgical damage resulting in lessrejects per the same work cycle or less rejects in general. A furthercriterion is the total work pieces ground per useful life of anequivalent grinding wheel.

It has now been found that using a novel wheel impregnant composition incombination with a porous wheel, in whose interstices the impregnant ismore uniformly and thoroughly dispersed than heretofore possible withsulphur impregnated wheels, extended wheel life is achieved, while atthe same time specified tolerances of the work piece have beenmaintained throughout an extended work piece grinding cycle. Moreover,this result has been achieved with improved surface finish. Also, priorart problems associated with using sulphur impregnated wheels, such assulphur staining of work pieces, wear of diamonds in dressing wheels byinteraction with sulphur, sulphur contamination of cutting fluids, andodoriferous gases given off by sulphur, etc., have been eliminated and/or minimized. As a result of the novel impregnant, other benefits havebeen obtained, such as increased safety factor due to less stressassociated with diminished loading of the wheel; e.g., under constantforce grinding operations.

It is an object of the present invention to provide an abrasive articlegiving improved grinding properties. It is another object of theinvention to provide a vitrified abrasive grinding wheel whoseinterstices have been uniformly and thoroughly impregnated with acomposition that confers improved grinding properties on the wheel,especially when the wheel is used for grinding operations heretoforerequiring sulphur or sulphurized fats as impregnants. It is stillanother object of the invention to provide a vitrified bond abrasivegrinding wheel which exhibits an improved life cycle, provides animproved finish to the work piece surface being ground, prolongs theuseful life of a diamond dresser. It is still a further object of thisinvention to provide an impregnant consisting essentially ofN,N'-alkylene bis-stearamide which resists migration during the workcycle from a vitrified bond,

aluminum oxide abrasive grinding wheel which wheel is suitable forinternal first grind and finish grind purposes. Other objects of theinvention will-be in part obvious and in part pointed out hereafter.

The present invention is predicated on the surprising discovery that anN,N'-aliphatic or aromatic diamide of an aliphatic or aromaticcarboxylic acid, more specifically N,N'-alkylene bis-stearamide, or moreparticularly, N,N'- ethylene bis-stearamide possesses exceptionallyuseful properties as an impregnant in vitrified bond abrasive grindingwheels.

The amides mentioned above and used as the impregnants are derived froma diamine and a carboxylic acid of the acids and amines listed below. Asa diamine, the following diamines are useful: aliphatic diamines such asalkylene diamines; e.g., ethylene diamine, propylene diamine,tetramethylene diamine, diethylene triamine, 1,6- hexane diamine;cycloaliphatic diamines; e.g., piperazine, cyclohexyl bis 1,4-methyldiamine; aroma-tic diamines; e.g., p-phenylene diamine, toluene diaminessuch as metatoluene diamine, xylylene diamine such as meta-xylylenediamine; menthane diamine. As a carboxylic acid, the following acids areuseful: azelaic, adipic, arachidic, capric, caproic, caprylic, behenic,cerotic, pelargonic, undecanoic, lauric, myristic, palmitic, stearic,lignoce-ric, oleic, sebacic, succinic, isosebacic, ricinoleic,12-hydroxystearic. Useful aromatic acids are benzoic acid naphthenicacids, phthalic acids, etc. Of the above amides those derived fromalkylene diamines and aliphatic acids are preferred. Of the last, theamides derived from ethylene diamine and fatty acids are most suitable.In all cases the amides still have to possess a melting point of atleast 225 F. and preferably a melting point of at least 280 F. The mostpreferred melting point range which characterizes the most desirableamides is about 290 F. and higher.

Although a number of the above-mentioned carboxylic compounds do notexist in pure state but are associated with different mixtures, it isvery easy to determine the melting point of these mixtures andconsequently the acceptability of the amides as a novel impregnant. Anillustrative list of the amide compounds and mixtures of materialshaving acceptable melting point properties are: stearic acid and adipicacid amides of ethylene diamine; stearic acid and azelaic acid amides ofethylene diamine; caprylic acid and capric acid amides of ethylenediamine; benzoic acid amide of ethylene diamine; stearic and sebacicamides of ethylene diamine; caproic acid amide of ethylene diamine; amixture of stearic acid and acetic acid amides of ethylene diamine;pelargonic acid amides of ethylene diamine; myristic acid amide ofethylene diamine; azelaic acid amide of meta-toluene diamine; stearicacid and azelaic acid amine of 1,6 hexanediamine; stearic acid amide ofp-phenylene diamine; sebacic acid amide of meta-xylylene diamine and thelike.

As a consequence of this invention, prior art impregnants such assulphur or compositions requiring multiple components can now bereplaced by a single component. Moreover, the preferred N,N'-ethylenebis-stearamide, which is a mixture of stearic and palmitic acids,should, in its most desirable form, consist of a mixture removed fromits eutectic melting point of 280 F. by at least 10 F. and thus shouldhave a melting point of approximately 290 F. or higher.

In carrying out the present invention, any suitable and well-knownabrasive material may be used; e.g., aluminum oxide (A1 carbides such assilicon carbide (SiC), fused zirconia (ZrO mixtures of zirconia andalumina (l045% ZrO 90-S5% A1 0 and the like. Of the above, aluminumoxide is preferred.

These abrasive materials may be selected in various grit sizes ormixtures thereof, preferably of a grit size of 54 and finer and of thegrades and structures commonly employed in vitrified grinding wheels.

A number of internal grinding wheels were madeincorporating thefollowing compositions of grit types. Conveniently, aluminum oxide waschosen, although the other mentioned abrasives may be used.

The compositions are as follows:

(A) A semi-friable aluminum oxide,

(B) A friable aluminum oxide.

(C) A very friable aluminum oxide (white).

(D) A friable aluminum oxide, less friable than composition B.

These compositions were selected in the following grit sizes:

and admixed with a ceramic powder comprising a formulation to give thevitreous bond. A suitable ceramic powder comprises, for example, ballclay, feldspar, borosilicate frit or the like components.

From this mixture, green grinding wheels of various shapes were formedinto desired configurations and fired at a temperature above about 2,000F. to form a highly porous, hard structure. The pores may typicallycomprise as much as 40% of the volume of the wheel.

Next, the abrasive wheels, preheated to approximately 350 F. to 375 F.,were partially immersed in melted N,N'-ethylene bis-stearamide and heldat about 290 F. to 325 F. or higher, depending on the melting point ofthe other amides if other amides are used. Capillary action caused auniform wettin and impregnation of the wheel without entrapping of airinto the wheel interstices. Op tionally a vacuum was applied to aid theremoval of air from the interstices of the wheel, and thus aiding theimpregnation. After this, the wheels were removed from the impregnantplaced on absorbent paper, inverted and allowed to cool at roomtemperature. Alternatively, the impregnants in form of a powder and thewheels are placed in a vessel without preheating. The vessel is thenheated and held in an oven at 310 F. After allowing the wheels to soakup the amide, they are removed from the amide and allowed to cool. Thesewheels were compared with the same type of abrasive wheel as furtheridentified herein and impregnated with sulphur.

In order to point out more fully the nature of the present invention,the following specific examples are given of illustrative embodiments ofthe present impregnant showing the preparation and use of the abrasivearticle as Well as the improved grinding method and results.

EXAMPLE I A 6-inch by 12-inch railroad axle bearing cone taper and ribswere ground simultaneously in a microcentric operation using a 20-inchby Z-inch wheel. Two wheels were used having grit composition asindicated above with a grit size of 54; and two wheels were used withthe same grit composition and a grit size of 60. One of the identicalwheels of the specified grit size had as an impregnant N,N-ethylenebis-stearamide and the other had as an impregnant sulphur. When usingthe wheels containing the amide at a stock removal amount of .025 inchon the taper and .007 inch on the ribs of the axle bearing cone, sevenwork pieces could be ground to satisfactory tolerances before a45-second diamond dress of .0015 inch was required for the wheel.Contrarywise, only three work pieces could be ground to satisfactorytolerances with the sulphur impregnated wheel before the same dress wasrequired. Moreover, when the number of work pieces was increased fromthree to more than three for the sulphur impregnated wheel, chatter,overheating, and excessive power requirements develop.

EXAMPLE II A number of the impregnated wheels were picked for grindingof roller or ball bearing tracks and bores of bearing races. These Workpieces were roughly finished with identical abrasive wheels of gritcomposition D having a grit size of 100 except that for comparisonpurposes, one group was impregnated with sulphur and the other 'wasimpregnated with N,N-ethylene 'bis-stearamicle. Thereafter, these workpieces were finished with identical wheels made of abrasive gritcomposition B having a grit size of 120. Finishing efliciencies of thewheels were expresed in R.M.S. defined as the square root of the mean ofthe sum of the squares of the height in microinches of surfaceirregularities. In order to obtain a measure of the work piece finishingability of the two types of wheels, R.M.S. values were taken across thefinished bearing track. This value is read from a recording-instrument.To show the ability of the wheel to perform in an acceptable mannerthroughout its grinding life, the finishing efiiciency of a newwheel'and an old Wheel was determined in a similar manner. For thispurpose a new wheel may be defined as an unused wheel of maximum usablediameter. An old wheel may be defined as a used wheel of smallest usablediameter. In the table to follow, the data illustrate the superior workpiece finishing ability of the wheel impregnated with the novelimpregnant.

TABLE I.GRINDING OF BEARING SURFACES FINISHING ABILITY R.M.S. of 1stPart R.M.Sfot 5th Part Cycle time .399 minutes.

Wheel A was impregnated with N,N-ethylene bis-stearamide. Wheel B wastreated with sulphur which also caused random sulphur staining of thework pieces.

EXAMPLE III Wheel of various sizes and configurations were used forgrinding bearing cups and cones. These wheels were of composition D andof a grit siZe of 80. A number of wheels were impregnated with the novelgrinding wheel impregnant and a number with sulphur. These wheels wererun on a variety of grinding machines, such as Heald machines Model Nos.1CF90, 290A, 180, 188A and 81 made by the Heald Machine Co., Worcester,Mass. Operating conditions were identical for grinding wheels havingboth types of impregnants. In Table II to follow, the finish wasmeasured and recorded for the high R.M.S. reading across the bearingtrack. Different machine parts were ground with the difierent wheels,but both types of irnpregnants were tested on the same machine. Bothcontrolled feed rate and controlled force conditions were used. Surfacefinish and part geometry were maintained well within printspecifications. Representative results are illustrated below. Wheelsdesignated by A are impregnated with N,N'-ethylene bis-stearamide, whilethose designated by B are sulphur impregnated.

TABLE II.-COMPARISON OF GRINDING PERFORMANCE OF NOVEL WHEELS AND WHEELSIMPREGNATED WITH SULPHUR UNDER IDENTICAL OPERATING CONDI- TIONS Totalwork Finish Heald type Wheel pieces per R.M.S.-high machine type Wheelsize, inches wheel reading 1% x 1% x V; 155 38 EXAMPLE IV Anotherprocedure was carried out whereby the performance of differentimpregnants was compared when grinding outer bearing races of 52100steel with an internal grinder (Heald 1CF91) with a low force value of20 lbs. and with a high force value of lbs. An untreated standard wasalso used. These wheels were of grit composition D (previouslymentioned) with a grit size of of medium grade and structure having avitrified bond. Used as irnpregnants were: (a) sulphur, (b) N,N'-ethylene bis-stearamide and (c) a mixture of about 80% sulphurized fat,10% mineral oil and 10% of a composition as in (b). The sulphun'zed fatis obtained by heating a quantity 'of unsaturated organic natural fat(generally an ester of glycerine) and sulphur until complete reactionbetween the sulphur and fat takes place leaving no free fat. About 20%reacted sulphur on basis of fat is the maximum which can be achieved.

For each composition compared, fifty work pieces were ground. Each wheelwas dressed at the beginning of the operation and after twenty-five workpieces. Stock removal was about .005 inch on the diameter. Finish on thework pieces was obtained in R.M.S. using a profilometer while thesurface finish range (high reading) was determined for the first tenWork pieces. Metal damage was obtained using Nytal etch test.

Results of these tests are summarized in the following table:

TABLE IIL-COMPARISON OF IMPREGNANTS Grinding fluid A is a heavy dutycutting and grinding fluid of soluble oil emulsion containing fat,sulphur and chlorine conventionally employed in the industry.

In a similar manner, the same work pieces were ground with aconventional heavy duty grinding oil having a viscosity of 100 SUS at100 F. and similarl containing sulphur, chlorine and fat. The surfacefinish of the work pieces were superior when ground with wheelsimpregnated with composition (b) as against the unimpregnated controland wheels impregnated with sulphur and composition (c).

Similar, acceptable results were obtained using amides of ethylenediamine and caprylic acid and ethylene diamine and pelargonic acid.

Subjecting the work pieces to a staining test also showed the novelimpregnant to possess superior properties. For example, when immersingwork pieces in a grindingcoolant fluid of the conventional type whichfluid contained the solid material from each of the pulverized grindingwheels having as impregnants sulphur and the compositions (b) and (c),the work piece in fluid containing the novel impregnant did not stain,while the sulphur-containing wheel material and the wheel material ofcomposition (c) stained the work pieces after a twoweek immersion.Staining was evident by the development of a tan to brown color.

The novel wheel and impregnant combination is suitable in most grindingoperations, such as internal, centerless, plain, surface, disk,centertype, shoe-type centerless, etc.

From the above examples, such as Example I, it is evident that the novelimpregnant extends wheel life and thus allows production of more workpieces per dress. Specified print tolerances can be easily maintained asdemonstrated by the data in Tables I and H. For given surface finish,greater operating safety margins are obtained; e.g., at constant forceconditions less stress is set up in the wheel, such as when surfaceloading is absent (characterized also by metallurgical damage).Conversely, less rejects are produced because surface finishes areimproved. Sulphur staining of parts and metallurgical damage to 7 partsis absent when using the novel impregnant as demonstrated in Example IV.These results are surprising, because the impregnant consistsessentially of N,N-ethylene bis-stearamide. Other unexpected advantagesare the ability to stub down; i.e., reduce the wheel size, or use wheelsof reduced size on other machines or other applications. As aconsequence a large inventory of wheels of different sizes can bereduced.

Moreover, the different grinding methods illustrated herein are improvedby the use of the novel wheels impregnated with the N,N' ethylenebis-stearamide when this impregnant is presented to the work pieceduring a grinding operation. I

Itis, of course, to be understood that the foregoing examples areillustrative only, and that numerous changes can be made in theingredients and properties described therein without departing from thespirit of the invention as defined in the appended claims.

What is claimed is:

1. A grinding wheel comprising abrasive grits, a vitri- -fied bondholding said grits together to form the grinding wheel, said wheelhaving an interstitial space which space contains essentially an amideof a diamine and carboxylic acid having a melting point of at least 225F. and wherein the diamine is an aliphatic diamine, a cycloaliphaticdiamine, or an aromatic diamine. V V V 2. A grinding wheel according toclaim 1 wherein the amide melts at above 280 F. and is derived from acycloaliphatic diamine and an aliphatic acid.

3. A grinding wheel according to claim 1 wherein the amide melts above280 F. and is derived from an alkylene diamine and an aliphatic acid.

4. A grinding wheel according to claim 1 wherein the amide melts above280 F. and is derived from an aro-' matic diamine and an aliphatic acid.

5. A grinding wheel comprising abrasive grits, a vitrified bond holdingsaid grits together to form the wheel according to claim 1, said wheelhaving an interstitial space which space contains essentiallyN,N-etl1ylene bisstearamide.

. 6. A grinding wheel according to claim 1 comprising aluminum oxideabrasive grains, a vitrified bond hold- 8 ing the grains together toform a wheel, said wheel having an interstitial space containingessentially N,N'- ethylene bis-stearamide.

7. A grinding wheel according to claim 1 comprising aluminum oxideabrasive grains, a vitrified bond holding the grains together to form awheel, said wheel having an interstitial space containing essentiallyN,N-ethylene bis-stearamide of a melting point in excess of about 290 F.

8. In an improved grinding method wherein an abrasive wheel has aninterstitial space constituent and wherein said wheel is presented to awork piece and engaged therewith, the work piece ground, and the wheeldressed after a work cycle during which at least one work piece isground, the improvement comprising the step of maintaining in the workcycle the abrasive wheel in contact with the work piece in presence ofan amide of a diamine and a carboxylic acid as the major essentialinterstitial space constituent of said wheel wherein the diamine is analiphatic diamine, a cycloaliphatic diamine, or an aromatic diamine, andwherein the amide has a melting point of higher than 225 F.

9. In an improved grinding method according to claim 8, wherein theamide melts above 280 F. and is derived from an alkylene diamine and afatty acid.

10. In an improved grinding method according to claim 8 wherein theinterstitial space constituent is N,N- ethylene bis-stearamide which ischaracterized as having a melting point of 290 F.

I References Cited UNITED STATES PATENTS 1,403,416 1/ 1922 Katzenstein51295 2,421,623 6/1947 Kistler 51295 2,544,641 3/1951 Coes 51-2953,295,940 1/1967 Gerow 51-295 3,321,287 5/1967 Hunsberger et a1. 51-295DONALD J. ARNOLD, Primary Examiner US. Cl. X.R.

